Belt retractor with switchable force limiter

ABSTRACT

The invention relates to a belt retractor ( 10 ) with a switchable force limiter. Said belt retractor ( 10 ) comprises as the force limiter at least one energy absorbing element ( 13; 14, 15; 61 ) that is linked with the reel shaft ( 12 ) and with the locking device of the belt retractor ( 10 ) via a profiled bead ( 50 ). The belt retractor is further provided with a switch device with which the energy absorption is adjusted. The aim of the invention is to provide a switch device that functions independent of the transmission of power between the reel shaft and the torsion bar. Said switch device (latch  21 ) is designed in such a manner that it can be switched at any time during the already existing energy absorption via the drive ( 26 ) that is independent of the reel shaft ( 12 ) and/or the switch device.

BACKGROUND OF THE INVENTION

The present invention relates to a belt retractor provided with a forcelimiter, whereby the belt retractor has as a force limiting device atleast one energy absorbing element that is linked to the spool and via aprofiled head to the blocking apparatus of the belt retractor and aswitching device is provided that adjusts the energy absorption and thatis switchable via an independent drive. Such belt retractors can bedesigned both as self-blocking belt retractors with a vehicle-sensitiveand/or belt-sensitive controllable blocking apparatus and as so-calledlimit fitting in accordance with EP 0 773 147 A2.

WO 97/49583, which forms the generic type, describes a self-blockingbelt retractor with the features specified in the foregoing; in theexemplary embodiments individually detailed therein provided as energyabsorbing element is a torsion bar with two or three sections switchedone after the other, and also described is the arrangement of two energyabsorbing elements switched parallel to one another. The associatedswitching device can only be switched under a load that is, can only beswitched given the application of great actuating forces when energyabsorption has already been turned on, because an existing force- orload-transferring coupling between the spool and torsion bar has to beovercome, i.e., there must be a switch to such a coupling. The designand operative complexity required for this is correspondingly high. Theobject of the invention is therefore to provide in a belt retractorhaving the generic features a reliable switching device that worksindependently of a force transfer already existing between spool andtorsion bar.

This object is achieved including advantageous embodiments and furtherdevelopments of the invention from the contents of the patent claimsthat follow this specification.

SUMMARY OF THE INVENTION

The basic idea of the invention is that the switching device, which canbe switched at any time via the drive arranged independent from thespool and/or switching device has a pawl borne with a tendency to openthat is held in its coupling position by means of a to spool ring thatis displaceable in the direction of the spool axis, and in that thespool ring can be axially transferred by means of a pyrotechnicallydrivable adjusting apparatus into a position in which the spool ringmakes it possible to reverse the pawl from its coupling position to itsrelease position. Since the at least one pawl for connecting the torquetube and the spool is borne with a tendency to open, no more actuatingforces occur for moving the pawl once the pawl has been released by thedisplacement of the spool ring.

In accordance with one exemplary embodiment of the invention, it isprovided that at least two energy absorbing elements are providedarranged in series or parallel to one another, and that the switchingdevice switches from one energy absorbing element to the other energyabsorbing element when the drive is triggered.

In accordance with another exemplary embodiment of the invention, it isprovided that the torsion bar has at least two sections with differentcross-sections arranged in series to one another for a establishing adifferent energy absorption, and a torque tube is provided that connectsat least one section of the torsion bar and the spool in a form-fit, assuch a design of a belt retractor is known in principle from WO97/49583.

In an alternative embodiment of two energy absorbing elements, it can beprovided that a torsion sleeve is arranged connected in switchedparallel to the torsion bar, and torsion sleeve or torsion bar can beswitched off by means of the switching device allocated to the torsionsleeve and that allocated to the torsion bar.

In accordance with one exemplary embodiment of the invention, it can beprovided that the spool ring is connected to the spool via form-fitdesigns and rotates together with it.

In particular, it can be provided that the pawl is pivotably borne in arecess in the cross-section of the spool, and the spool ring is arrangedspanning the exterior circumference of the spool such that the spoolring in its position maintaining the pawl in its coupling positioncovers the recess.

For effecting the change in position of the spool ring, it can beprovided that the control apparatus comprises a set collar that isarranged on the belt retractor rotatable under the effect of a driveacross a limited area of rotation for displacing the spool ring and thatis supported against a cover of the belt retractor by at least one rampinclined in the axial direction of the spool and that can be displacedaxially due to its twisting, whereby in accordance with one exemplaryembodiment of the invention a plurality of ramps are distributed acrossthe circumference of the set collar and the cover. Such a controlapparatus is associated with the advantage of an additionalservo-effect, since due to the helical movement produced in this manneronly a small radial force must be applied in order to produce a muchgreater axial force for displacing the spool ring and therefore forproducing the switch movement under a load.

With regard to the design of the drive for rotating the set collar, alinearly displaceable pyrotechnically driven piston can be provided thattangentially impacts a shoulder projecting radially from the set collar.This stationary external arrangement of the pyrotechnic drivesubstantially simplifies the electrical control, since it is notnecessary to transfer electrical signals to the rotating spool and thepyrotechnics attached thereto.

The inventive coupling between torque tube and spool makes it possiblein accordance with one exemplary embodiment of the invention to arrangea deformable element between spool and torque tube. In accordance withexemplary embodiments of the invention, the deformable element can bedesigned as shearing bars extending in the circumferential direction ofspool and torque tube or as bending bars arranged radially between spooland torque tube. In an additional embodiment of the invention it can beprovided that the deformable element is designed as bending barsarranged radially between spool and torque tube. This ensures a gentletransition from the first force level to the other force level.

With respect to the cooperation between the belt force limitationcreated in the belt retractor and the airbag located in the vehicle, thepoint in time at which the switch takes place from the higher forcelevel to the lower force level is very important. For a control in thisregard, in accordance with one exemplary embodiment of the invention itis provided that for igniting the drive for the control device a timeswitch is provided that is activated by the vehicle sensor and thatinvolves a pre-selected period of time. In this exemplary embodiment ofthe invention, the ignition occurs at a pre-specified point in timeindependent of other accident conditions.

In an alternative embodiment of the invention it is provided that adevice is provided for determining the revolutions of the spool under aload after a pre-selected threshold has been exceeded for determiningthe belt withdrawal effected by the force limitation, and the ignitionof the drive for the set collar occurs when a pre-selected beltwithdrawal has been achieved. In this embodiment of the invention, thebelt withdrawal occurring during the accident and caused by the effectof the force limiting device of the belt retractor is used as a measurefor switching the level of the force limiting device.

BRIEF DESCRIPTION OF THE DRAWING

The drawings illustrate exemplary embodiments of the invention that aredescribed in the following: In the drawings:

FIG. 1 is longitudinal view of a belt retractor with spool and atwo-stage torsion bar including the switching device that has a firstswitch state (release of the pawl);

FIG. 1A is the subject of FIG. 1 illustrated with the parts in anexploded view;

FIG. 2 is the switching device in accordance with FIG. 1 in a frontalview along the line A—A;

FIG. 3 is a schematic representation of the drive for the switchingdevice;

FIG. 4 is the switching device in accordance with FIG. 2 after the drivehas been actuated;

FIG. 5 is the switching device in accordance with FIG. 2 with additionalshearing bars for adjusting an additional damping effect;

FIGS. 6a, b are the switching device in accordance with FIG. 2 with anadditional bending bar;

FIGS. 7a, b are the switching device in accordance with FIG. 2 with astrip-type deforming element;

FIG. 8 is the subject of FIGS. 1 and 3 in connection with a control ofthe switching time of the switching device as a function of the beltwithdrawal in a second switching state (blocking the pawls);

FIG. 9 is another exemplary embodiment of a belt retractor in accordancewith FIG. 1 with two parallel-switched energy absorbing elements.

DESCRIPTION OF PREFERRED EMBODIMENTS

The belt retractor 10 visible in FIGS. 1 and 1A has a U-shaped frame inthe lateral legs 11 of which a belt shaft or spool 12 is rotatablyborne. A safety belt 9 is wound on the spool 12. Located in the interiorof the spool as force limiting device is a torsion bar 13 that has asection 14 with a larger cross-section and a section 15 with a smallercross-section, whereby provided between the sections 14, 15 and on theexterior end of the section 15 of the torsion bar 13 are connectingparts 16 a, b by means of which the spool 12 is attached to the sections14 and 15 of the torsion bar 13. On the exterior left side of theillustration in FIG. 1 is the blocking side 17 of the belt retractor, atwhich the torsion bar 13 is attached to a profiled head 50.

The spool 12 is coupled to the section 14 of the torsion bar 13 havingthe larger cross-section via a torque tube 18 that covers in a form-fitthe associated connecting part 16 a, while for connecting the spool 12to the section 15 of the torsion bar 13 having the smaller diameter thespool 12 covers directly in a form-fit the connecting part 16 b arrangedon the right-hand end of the section 15. The switching device forswitching the force limiting device from the higher force level to thelower force level is formed via pawls 21, shown in detail in FIG. 2,that couple the spool 12 and the torque tube 18 in a manner to bedescribed such that when the pawls 21 are in the coupled position theforce flow from the spool 12 via the torque tube 18 to the section 14 ofthe torsion bar 13 occurs such that when there is a corresponding loadon the spool 12 from the pull exerted on the safety belt 9 the section14 twists and makes possible the force limitation at a high level. Ifthe pawls 21 are disengaged from the torque tube 18 by the actuation ofthe switching device which is yet to be explained, the spool 12 canrotate relative to the torque tube 18, and now the force flow occurs viathe form-fit connection between the spool 12 and the connecting part 16b allocated to the section 15 of the torsion bar 13, so that the section15 twists and the force can be limited at a lower level.

As can be seen in FIG. 2 in conjunction with FIG. 1a, the pawls 21effecting the coupling between spool 12 and torque tube 18 in theircoupling position are borne in a recess 40 formed in the cross-sectionof the spool 12 such that they can pivot about a center of rotation 22,whereby the spool 12 is surrounded on its exterior circumference by aspool ring 45 that spans the recesses 40 in the spool 12 and thereby viasupports 24 holds the pawls 21 at their engaging noses 23 engaged withthe recesses 51 of the torque tube 18. If the spool ring 45 is displacedin the axial direction, the pawls 21 are released from the support 24 ofthe spool ring 45 so that the pawls 21 that are borne with a tendency toopen pivot outward into the recess 40 and thereby eliminate theconnection between the spool 12 and the torque tube 18. The tendency toopen that the pawls 21 have is adjusted via appropriate designs of therecesses 51 and of the engaging nose 23. The spool ring 45 is borne onthe spool 12 in a form-fit via noses 52 engaging in the profile of thespool 12 and rotates with the spool 12.

The axial displacement of the spool ring 45 is introduced via the driveillustrated in FIG. 3, in which arranged in a cover 20 of the beltretractor 10 that covers the spool end is a drive 26 with a pyrotechniccharge 27 that impacts a piston 28, causing its linear movement. In itslinear movement, the piston 28 acts on a shoulder 29 projecting radiallyfrom a set collar 19 such that the set collar 19 is caused to rotatewhen the piston 28 is actuated. The set collar 19 is borne on thehousing 10 or on the cover 20 that is attached to the housing 10 anddoes not also rotate during the normal function of the spool 12.However, it can perform a limited rotational movement during itsadjusting motion. The set collar 19 is supported against the cover 20 byinclined ramps (not shown in detail) arranged between set collar 19 andcover 20 so that due to the introduced twisting of the cover 20 the setcollar 19 is pressed and thus axially displaced. This axial displacementof the set collar 19 is transferred to the spool ring 45 via theadjacent positions of the set collar 19 and spool ring 45 such that thedisplacement of the spool ring 45 leads to the release of the pawls 21,as described and illustrated in FIG. 4. In the illustrated exemplaryembodiment, spool ring 45 and set collar 19 rest against one another viaoverlapping members so that the axial displacement of the set collar 19is correspondingly transferable to the spool ring 45.

As can be seen in detail in FIGS. 5 through 7, in accordance withexemplary embodiments of the invention it is provided that an additionaldeformable element is arranged between the torque tube 18 and the spool12 so that during the switching process from the higher level of forceto the lower level of force of the torsion bar there is an additionalgradation of the force transfer, that is, there is a more gentletransition; thus, with a two-stage torsion bar it is possible to set anadditional third force characteristic. That is, if the pawls 21 pivot sothat the spool 12 is uncoupled from the torque tube 18, during thefurther process while the section 15 of the torsion bar 13 is beingswitched to the spool 12 there is a relative rotation of the spool 12 tothe torque tube 18, and at the beginning of this relative rotation athird energy absorbing element is switched on via deformable elementsthat are additionally arranged between the spool 12 and the torque tube18 and that at the beginning of the switch to the lower force levelfirst cause an additional dampening that occurs parallel to the section15 of the torsion bar 13 via the provided deformable elements before, inthe further process, there is force limiting only via the section 15 ofthe torsion bar 12.

In the exemplary embodiment illustrated in FIG. 5, arranged betweenspool 12 and torque tube 18 are two shearing bars that shear off duringa relative rotation of the spool 12 to the torque tube 18.

In the exemplary embodiment illustrated in FIGS. 6a and 6 b, tworadially arranged bending bars 31 are provided that at their one end arein a recess 32 of the spool 12 and at their other end are adjacent to amember 33 on the torque tube 18 so that during a relative rotationbetween spool 12 and torque tube 18 the bending bars 31 first are bentinto a free space 34 formed on the spool 12 before the section 15 of thetorsion bar becomes effective due to the further rotation of the spool12.

In the exemplary embodiment illustrated in FIGS. 7a, 7 a, formed in thespool 12 as deformable element is a strip 35 made of a deformablematerial that is inserted in a channel 36 and is suspended at its end onthe torque tube 18 and thus during a relative rotation between spool 12and torque tube 18 is pulled out of the channel while deforming beforethe spool 12 due to its uncoupling from the torque tube 18 whilecontinuing to rotate can engage the section 15 of the torsion bar 13.

For correct switching of the force limitation during an accident andthus for the interplay between the belt retractor equipped with a forcelimiter and an airbag arranged in the vehicle, the point in time atwhich the force limiter is switched is very important because the beltwithdrawal enabled by the force limiter to a certain degree causes apre-positioning of the belted person for whom the inflating airbag isintended.

Although not illustrated, it is possible to determine the best point intime for the switching process, that is, for igniting the pyrotechniccharge 27, to trigger this ignition across a specified point in time inthat a period of time is pre-selected in an appropriately providedcontrol unit, and after this period of time has elapsed the pyrotechniccharge 27 is ignited.

FIG. 8 illustrates an alternative option for the control in which thebelt withdrawal caused by the effect of the force limiting device of thebelt retractor is used as a measure for igniting the pyrotechnic unit27. In this case, a measuring device 37 is provided on the beltretractor 10, for instance in the form of a potentiometer thatdetermines the speed of the spool rotations or the angular velocity.When the value thus acquired exceeds a threshold value, this isidentified as the beginning of the force limitation, and further beltwithdrawal is detected via the potentiometer. The angular velocity ofthe spool 12 during normal, manual belt withdrawal when the safety beltis being put on and during blocking of the belt retractor issubstantially lower than when the force limiting device, that is, theenergy absorbing elements, have been triggered. The angular velocityduring the force limiting process is approximately ten times higher thanduring normal belt withdrawal. Stored in a control unit 39 provided onthe vehicle is a specific measure of belt withdrawal as a prerequisitefor igniting the pyrotechnic charge 27, and when in another providedbelt retractor control unit 38 the belt withdrawal speed determined bythe potentiometer equals the value pre-specified by the control unit 39of the vehicle, the control unit 38 initiates ignition of thepyrotechnic charge 27. At this point in time the force limiting devicethen switches from the higher force level to the lower force level.

Finally, FIG. 9 illustrates one exemplary embodiment of the inventionwith two energy absorbing elements oriented parallel to one another. Inthis exemplary embodiment, as well, the spool 12 is rotatably borne inthe housing legs 11. At the blocking-side end 17 of the belt take-upspool 13, the spool on its front side is allocated a profiled head 50that rotates in the U-shaped leg 11 of the housing, whereby borne on theprofiled head 50 is an anti-blocking member 55 that can be radiallydeflected under the effect of a control device (indicated but not shown)and that due to the control in the case of a delay is guided into theteeth arranged in the associated through-hole in the housing.

The profiled head 50 and the spool 12 are connected to one another by atorsion bar 13 acting as force limiting device in that the one end ofthe torsion bar 13 is connected in a form-fit to the profiled head 50and the other end of the torsion bar 13 running in the spool 12 isattached to the spool 12. The spool 12 widens beyond the lateral legopposite the blocking side 17 in order to form the recess 40 necessaryfor bearing the pawls 21. The first exterior pawl 21 borne on theoutermost end of the spool 12 engages a radially projecting flange 60 ofthe torsion bar 13 so that when the pawl 21 is blocked the spool 12 isconnected to the torsion bar 13. The pawl 21 is kept engaged by anassociated exterior spool ring 45, whereby a first set collar 19 is alsoallocated to the first spool ring 45.

Provided as additional energy absorbing element is a torsion sleeve 61that covers the torsion bar 13 and is attached to the profiled head 50and that also has adjacent to the flange 60 of the torsion bar 13 aradial flange 62, to which is allocated a second pawl 21 that is borneon the spool 12 and located in its recess 40 and that is kept engaged bya second spool ring 45, which is itself controllable by a second setcollar 19. With this arrangement, different levels of energy absorptioncan be controlled by controlling the two pawls 21.

The features of the subject of this document disclosed in the foregoingspecification, patent claims, abstract, and drawings can be essentialindividually and in any combination to realizing the invention in itsvarious embodiments.

The specification incorporates by reference the disclosure of Germanpriority document 199 27 427.4 filed Jun. 16, 1999 and PCT/EP00/05474filed Jun. 14, 2000.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

What is claimed is:
 1. A belt retractor comprising: a force limitingdevice in the form of at least one energy absorbing element which isconnected to a spool for a belt and is also connected via a profiledhead with a blocking apparatus of said retractor; a switching device foradjusting energy absorption, wherein said switching device is switchableat any point in time via a drive mechanism that is independent of atleast one of said spool and said switching device, wherein saidswitching device is provided with a least one pawl that is mounted so asto have a self-opening tendency; a spool ring for holding said at leastone pawl in a coupling position, wherein said spool ring is displaceablein a direction of an axis of said spool; and a pyrotechnically drivableadjusting means for axially transferring said spool ring into a positionin which said spool ring enables a changeover of said at least one pawlfrom the coupling position thereof into a release position thereof.
 2. Abelt retractor according to claim 1, wherein at least two energyabsorbing elements are provided and are disposed in series with orparallel to one another, and wherein said at least one pawl switchesfrom one of said energy absorbing elements to the other energy absorbingelement when said drive mechanism is triggered.
 3. A belt retractoraccording to claim 1, wherein a torsion bar is provided as an energyabsorbing element and is provided with at least two sections that havedifferent cross-sections and are disposed in series with one another forthe purpose of establishing a different energy absorption, and wherein atorque tube is provided that positively connects at least one of saidsections of said torsion bar and said spool.
 4. A belt retractoraccording to claim 3, wherein a deformable element is disposed betweensaid spool and said torque tube.
 5. A belt retractor according to claim4, wherein said deformable element is embodied as shearing bars thatextend in a circumferential direction of said spool and said torquetube.
 6. A belt retractor according to claim 4, wherein said deformableelement is embodied as bending bars that are radially disposed betweensaid spool and said torque tube.
 7. A belt retractor according to claim4, wherein said deformable element is a strip of deformable materialdisposed in a channel of said spool, and wherein one end of said stripis secured to said torque tube and upon rotation of said torque tube canbe pulled out of said channel accompanied by deformation.
 8. A beltretractor according to claim 1, wherein a torsion bar is provided as anenergy absorbing element, wherein a torsion sleeve is connected inparallel to said torsion bar, and wherein said torsion sleeve or saidtorsion bar can be switched off by means of said at least one pawl thatis respectively associated with said torsion sleeve and said torsionbar.
 9. A belt retractor according to claim 1, wherein said spool ringis connected with said spool via positively engaging elements androtates together therewith.
 10. A belt retractor according to claim 1,wherein at least one pawl is pivotably mounted in a recess in across-section of said spool, and wherein said spool ring spans an outerperiphery of said spool in such a way that said spool ring covers saidrecess when said spool ring is in its position where it holds said atleast one pawl in the coupling position thereof.
 11. A belt retractoraccording to claim 1, wherein said adjusting means, for a displacementof said spool ring, comprises a set collar that is disposed on said beltretractor and is rotatable over a limited range under the effect of saiddrive mechanism, and wherein said set collar is supported against acover of said belt retractor by at least one ramp inclined in the axialdirection of said spool and can be displaced axially via rotationthereof.
 12. A belt retractor according to claim 11, wherein a pluralityof ramps are distributed over a periphery of said set collar and saidcover.
 13. A belt retractor according to claim 1, wherein said adjustingmeans comprises a rotatable set collar, and wherein said drive mechanismfor rotating said set collar is provided with a linearly displaceablepyrotechnically driven piston that tangentially acts upon a shoulderthat radially projects from said set collar.
 14. A belt retractoraccording to claim 1, wherein for ignition of said drive mechanism forsaid adjusting means, a time switch is provided that is activated by avehicle sensor and involves a pre-selected period of time.
 15. A beltretractor according to claim 1, wherein a device is provided fordetermining revolutions of said spool under load after a pre-selectedthreshold has been exceeded for the purpose of determining beltretraction effected by said force limiting device, and wherein ignitionof said drive mechanism for said adjusting means is effected when apre-selected belt withdrawal has been achieved.